Kimberly Vernon, age 15, of Dover, Del., for her question:

WHAT CAUSES CONJUNCTIVITIS?

Conjunctivitis is any inflammation of the membrane covering the outer layer of the eyeball and the inner lining of the eyelids. This membrane is called the conjunctiva.

Because of conjunctivitis, the eyes may become red and watery and pus may form. It is caused by bacteria and viruses that can be spread to others by using the same towel.

Doctors usually cure bacterial conjunctivitis with antibiotics or sulfonamides.

Viruses that can infect the conjunctiva include those that cause colds and measles. Other viruses sometimes infect the conjunctiva and the cornea, which is the clear tissue over the colored part of the eye.

Sometimes the conjunctiva can become inflamed by smoke, certain eye drugs and substances that cause such allergies as hay fever.